TYPES OF MARINE POLLUTANTS

A. PRIORITY POLLUTANT

  • Substances that pose the greatest threat to marine environments as a result of their toxicity, persistence, bioaccumulation, or other unusual properties have been placed on priority pollutant lists of a number of countries.
  • The U.S. Environmental protection Agency (U.S. EPA) designated 127 chemicals as priority pollutants in the United States in the late 1970s. These chemicals are pollutants which have commonly occurred in discharged wastewaters and for which there were existing stocks of chemicals to make standard solution.
  • Trends Program is priority pollutants (Table 6). The 74 priority chemicals not measured by this program consist almost entirely of low-molecular-weight, highly soluble, volatile organics.
  • In England, The Red List of highest priority substances, initial priority chemicals of The Red List.
  • The long-term goal has been to reduce the environmental concentrations of these chemicals as much as possible regardless of their current levels.

B.COMMONLY OCCURRING POLLUTANTS

Common pollutants that have been reported from estuarine and marine environments include the following:

1. Excessive nutrients causing progressive enrichment and periodic eutrophication problems;

2. Sewage and other oxygen-demanding wastes (principally carbonaceous organic matter)which promote anoxia or hypoxia of coastal waters sub- sequent to microbial degradation;

3. Pathogens (e.g., certain bacteria, viruses, and parasites) and other infectious agents often associated with sewage wastes;

4. Petroleum hydrocarbons originating from oil tanker accidents and other major spillages, routine operations during oil transportation, effluent from no petroleum industries, municipal] wastes, and non-point runoff from land;

5. Polycyclic aromatic hydrocarbons entering estuarine and marine ecosystems from sewage and industrial effluents, oil spills, creosote oil, combustion of fossil fuels, and forest fires;

6. Halogenated hydrocarbon compounds (e.g., organochlorine pesticides) derived principally from agricultural and industrial sources;

7. Heavy metals accumulating from smelting, sewage-sludge dumping, ash and dredged-material disposal, antifouling paints, seed dressings and slimicides, power station corrosion products, oil refinery effluents, and other industrial processes;

8. Radioactive substances generated by uranium mining and milling, nuclear power plants, and industrial, medical, and scientific uses of radioactive materials;

9. Calefaction of natural waters, owing primarily to the discharge of con- denser cooling waters from electric generating stations;

10. Litter and munitions introduced by various land-based and marine activities;

I1. Fly ash, colliery wastes, flue-gas desulphurizationsludges, boiler bottom ash, and mine tailings;

12. Drilling muds and cuttings;

13. Acid-iron and alkali chemicals; 14. Pharmaceuticals; and

15. Suspended solids, turbidity.

1-Nutrient Enrichment

Eutrophication

  • Excessive nutrient input continues unabated in many regions of the world.
  • The anthropogenic flux of nutrients in rivers and the atmosphere in many regions of the world is equal to or greater than the natural flux.
  • Globally, river runoff and atmospheric deposition deliver approximately equal concentrations of nutrients to marine environments.
  • Toxic phytoplankton blooms termed “red tides” periodically develop and cause mass mortality of invertebrates and fish.
  • Nitrogen is the primary nutrient responsible for the eutrophication of temperate estuaries and coastal seas, while phosphorus appears to be critically important in many tropical estuarine and coastal system.
  • The accumulationof plant and animal remains on the seasfloor and their subsequent bacterial decay deplete bottom waters of oxygen, often to seriously low levels (i.e, anoxic conditions with 0 mg/1 dissolved oxygen and hypoxic conditions with <2.0 mg/1 dissolved oxygen).
  • Dissolved organic carbon concentration sin estuarine and coastal marine waters typically range from about 1 to 5 mg/1, and particulate organic carbon levels generally range from approximately 0.5 to 5.0 mg/1 in estuaries and 0.1 to 1.0 mg/1 in coastal seawater.
  • Bottom-water hypoxia may persist for months in some estuarine and shallow coastal marine systems where water column stratification inhibits vertical mixing. The intensity of water column stratification is a principal factor controlling the severity of dissolved oxygen depletion over broad areas.
  • Oxygen-depleted bottom waters impact benthic communities by producing acute changes in the distribution, abundance, and diversity of species. Nuisance organisms and opportunists may become dominant in an area, supplanting more desirable forms, such as commercially and recreationally important finish and shellfish.

(1)Increases in productivity

(2)Shifts in community dominants

(3)Development of anoxia in bottom waters.

(4)Losses of submerged aquatic vegetation.

  1. Organic Loading
  2. Sewage Discharges
  • Many eutrophication and organic loading problems in coastal regions throughout the world are linked to the discharge of sewage effluent and dumping of sewage sludge, respectively.

The goal of municipal treatment facilities which process domestic wastewaters is to reduce the content of the suspended solids, oxygen-demanding materials, dissolved inorganic compounds.

  • Complete treatment of municipal wastewaters involves a three-stage process (Figure 3).
  1. Stage 1, primary treatment, entails grit removal, screening, grinding, flocculation, and sedimentation. The liquid waste may then be processed in secondary treatment, and the sludge dumped at designated disposal sites.
  1. Stage 2, secondary treatment, focuses on the oxidation of dissolved organic matter and, hence, the removal of BOD. With 40-60% of the suspended solids and 20-40% of the BOD removed during primary treatment by physical methods, secondary treatment reduces the organic matter remaining in the liquid waste via aerobic bacterial attack.
  1. Stage 3, tertiary treatment, removes nutrients from the effluent. Additional steps may be taken to further improve effluent quality.
  1. Sewage Sludge
  • One of the principal products of municipal wastewater treatment is sewage sludge, a liquid waste containing up to 10% by weight of solid particles.
  • Controlled sewage sludge disposal in the ocean offers several advantages: (1) particulate organic waste mixes with seafloor sediments and is degraded by natural processes; (2) toxic substances are diluted to low levels and gradually buried under seafloor sediments; and (3) sludge dumping at sea is less expensive and generally safer than on land.
  • Between 1924 and 1987, virtually all sludge dumping in the United States occurred at inner – or mid-continental-shelf sites, which are now closed.
  • Between 1986 and 1992, substantial volumes of sludge were dumped at DWD -106 (Figure 5).
  • As noted previously, more than 30 million mt (wet) of sewage sludge have been dumped at DWD-106. Alternatives to sewage sludge dumping at sea have been implemented by most U.S. cities. Thus, it is likely that sewage sludge dumping at sea will continue to be a problem in the foreseeable future in some coastal regions.
  • The environmental effects of sewage sludge dumping at sea depends on the volume of sludge dumped, the types f pollutants contained in the sludge, and the hydrodynamic at the disposal sites.
  • The U.S. EPA has identified more than 100 chemical compounds of concern in sewage sludge; many of them are halogenated aliphatic and aromatic hydrocarbons, organochlorine pesticides, polychlorinated biphenyls, and phthalate esters.
  1. Sewage Impacted systems
  • There are several well-known sewage disposal sites in coastal waters of the United States and England.
  • On the west coast of the United States, Southern California shelf waters receive billions of liters of municipal wastewaters each day from a series of submarine outfalls.
  • Most of these wastewater (-90%) derive from the Hyperion Treatment Plant (HTP) of the City of Los Angeles, the Joint Water Pollution Control Plant (JWEPCP) of the County Sanitation Districts of Los AngelesCounty.
  • Adverse effects were observed on benthic communities and fish assemblages, with the greatest impacts observed on benthic infauna and commercial fishes.
  • Studies of the site in the early 1970s revealed classical effects of organic enrichment on the benthic fauna (i.e., decreases in species diversity, increases in pollution abundance and biomass.
  1. Other Organic Enrichment Sources
  • Two other important sources of organic enrichment in some estuarine and coastal marine waters that must be considered are wastes from waterfowl, wildlife, and aquaculture operations.
  • Nutrient enrichment from animal excretions (ammonia and urea) and fecl matter can cause nuisances phytoplankton blooms.
  • Possible acute effects of open-system aquaculture include the development for hypoxia, anoxia, and hydrogen sulfide, creating conditions inimical to estuarine and marine communities.
  • Structural changes in the benthos subsequent to sewage disposal are the basis of empirical models that describe the impacts of organic enrichment on marine benthic fauna. For example, macrobenthic communities subjected to increased organic loading, either spatially or temporally, will often exhibit:

(1) a decreases in species richness and an increase in total number of individuals attributable to high densities of a few opportunistic species;

(2) a general reduction in biomass, although there may be an increase in biomass corresponding to a dense assemblage of opportunists;

(3) a decrease in body size of the average species or individual;

(4) Shifts in the relative dominance of tropic guilds; and

(5) Shallowing of that portion of the sediment column occupied by infauna (6) Spatial and temporal gradients commonly develop at outfalls and dumpsites along which infaunal biomass, density, and species diversity change until unaffected conditions are observed

(7) it is conceivable that toxic chemicals associated with sewage wastes also may play a significant role in generating the benthic impacts.

  1. Oil
  1. General Impacts
  1. Noxious effects of oil pollution on marine communities are well chronicled, as are the damaging impacts on marine and coastal habitats.
  2. Crude oil consists of thousands of chemical compounds, many of which are toxic to marine life.
  3. Aliphatic and polycyclic aromatic hydrocarbon fractions of dissolved oil can decimate marine populations over extensive areas due to their extreme toxicity, rapid uptake by biota, and persistence in the environment.
  4. These fractions tend to bioconcentrate in marine organisms because of their high lipid solubility and are of major concern in commercially.
  5. Petroleum hydrocarbons sorb readily to particulate matter and accumulate in bottom sediments, where they may pose a chronic threat to the benthos.
  6. Water soluble compounds, such as benzene, toluene, and xylene, frequently kill macoplankton, ichthyuoplankton, or other life stages of organisms exposed to them in the water column, even at concentrations as low as 5 mg/.
  7. Polluting oil may physically smother marine organisms.
  8. Estuaries are especially sensitive to oil pollution. Benthic communities inthese systems usually suffer total or near total decimation immediately after major oil spills;
  9. Adverse effects of oil on estuarine and marine biota also occur indirectly via the degradation of critical habitat area and the decomposition of the oil.
  1. Crude Oil Composition
  1. Oil is classified as light, medium, or heavy.
  2. The relative concentrations of certain compounds in various categories have been effectively used to classify oil.
  1. Sources of Oil Pollution
  • Global crude oil production amounts to about 3 billion mt/yr, with approximately half of this total transported by sea. The quantity of oil entering marine waters each year from all sources (excluding biosynthesis) is estimated to be about 2.145 million mt (Table 10).
  • Maritime Organization reported a 60% reduction in oil pollution at sea between 1981 and 1989, attributable primarily to improvements in tanker operations and fewer accidental spills.
  • Further reductions will depend on future upgrades of shore-based installations (e.g., reception facilities) and decreases in the influx of oil from land-based sources.
  1. Fate of Polluting Oil
  • Various physical-chemical processes act within hours of an oil spill on the sea surface to alter its composition and toxicity, most importantly evaporation, dissolution, photochemical oxidation, advection and dispersion, emulsification, and sedimentation (Figure 7).
  • During the first 24-48 hr of an oil spill, evaporation and dissolution produce the greatest change in composition of the oil by causing the rapid loss of the lighter, more toxic and volatile components.
  • Photochemical oxidation acts on oil at or near the sea surface to convert high-molecular-weight aromatic hydrocarbons to polar oxidized compounds.
  • Agitation provided by waves and currents mixes the oil and seawater-leading to turbulence and dispersion of oil slicks.

1.As the heavier oil fractions mix with seawater, viscosity increases and a water-in-oil emulsion forms.

2. Viscid pancake-like masses called “chocolate mouse,: which develop from 50-80% water-in-oil emulsions may persist for months at sea.

3. Heaviest residues of crude oil – tar balls – measuring 1 mm to 25 cm in diameter are often advected, like chocolate mouse, to remove impact sites.

4. Oil is subject to biodegradation by many species of bacteria, fungi, and yeast. Bacteria are the most important biological agents in the breakdown process.

5. Four main approaches are followed in oil spill cleanup of marine environments:

(1) chemical applications;

(2) mechanical cleanup;

(3) shoreline cleanup;

(4) no spil control.

  • The most appropriate treatment option hinges on conditions existing at the cleanup site.
  • Chemical treatment of an oil slick usually involves the spraying of dispersants from ships or aircraft to accelerate the emulsification of the oil. Solvents and agents that reduce surface tension are also utilized to remove oil slicks from the surface of pools and enclosed inshore areas. However, dispersants are not effective on heavy or weathered oils, and some of them nay be toxic to marine life.16
  • Devices that physically contain floating oil are of great value in cleanup efforts in harbors and inshore regions.
  • When oil is stranded on beaches or rocky intertidal area, cleanup crews often enact physical removal procedure. Rocky surfaces may be cleaned by high-pressure hoses, high-pressure steam, hand-scrubbing techniques, or dispersants.
  1. Effects on Biotic Communities
  • Dramatic changes in benthic communities occur along rocky shorelines, estuaries, and shallow coastal marine environments exposed to polluting oil.
  • Low-energy habitats likely to trap oil, such as salt marshes, mangroves, and sea grasses, are generally teeming with life. Once the oil permeates through the bottom sediments, it creates long-term hazardous conditions that threaten the overall stability and health of the benthos.
  • Low oxygen concentrations in deeper sediment layers hinder bacterial degradation of the oil.
  • The rate of recovery of an intertidal or shallow subtidal marine habitat is controlled by the number of oiling events and the depth of oil penetration into the substrate.
  • Shallow-rooted annuals with limited food reserves are much more susceptible to oil pollution than perennials with.
  • The magnitude of oil impacts on estuarine and marine organisms is contingent upon many factors, the most notable being

(1) The amount of the oil;

(2) Composition of the oil;

(3) Form of the oil (i.e., fresh, weathered, or emulsified);

(4) Occurrence of the oil (i.e., in solution suspension, dispersion, or adsorbed onto particulate matter);

(5) Duration of exposure;

(6) Involvement of neuston, plankton, nekton, or benthos in the spill or release;

(7) Juvenile or adult forms involved;

(8) Previous history of pollutant exposure of the biota;

(9) Season of the year;

(10) natural environmental stresses associated with fluctuations in temperature, salinity, and other variables;

(11) types of habitat affected; and

(12) cleanup operations (e.g., physical methods of oil recovery and the use of chemical dispersants).

  • Organisms which are trapped, smothered, and suffocated by an oil spill. Those individuals surviving the physical impact of the oil may lose normal physiological or behavioral function if coated, thus predisposing them to greater long-term risk of death.
  • Sub-lethal effects, such as the impairment of organisms to obtain food or to escape from predators after being coated by the oil, likewise increase mortality of individuals within day or weeks of a spill.
  • Fish tend to avoid oil spills because they can swim. Hence, immediate impacts on fish populations may not be apparent.
  • Mammals and seabirds exhibit an array of response to oil. Sub-lethal effects chronicled in marine mammals include gastrointestinal and blood disorders, respiratory problems, changes in enzymatic activity in the skin, renal deficiencies, interferences with swimming, eye irritation.
  1. Polycyclic Aromatic Hydrocarbons
  1. Sources and Concentrations
  • PAH compounds originate from a variety of anthropogenic sources (e.g., municipal and industrial effluents, creosote, oil spills, urban and agricultural runoff, and fossil.
  • Incomplete combustion of organic matter, especially in the high temperature (500-800oC) range, is a primary mechanism for atmospheric contamination by PAH compounds, many of which enter marine waters via fallout.
  1. Distribution

PAHs in Estuarine and Coastal Marine Environments

  • The transport of PAHs to marine environments occurs via surface waters and the atmosphere.
  • Bottom sediments of estuaries and near shore coastal marine waters located near urban and industrial centers serve as major repositories of PAHs.
  • Because of the strong affinity of PAHs for sediments and other particulate matter, they accumulate too much higher concentrations on the seafloor than in overlying waters.
  • The concentrations of PAHs in seafloor sediments usually exceed those in the water column by a factor of 1000 or more.
  1. Effects on Biotic Communities
  • Polycyclic aromatic hydrocarbons adversely affect marine life as revealed by both laboratory experiments and field observations. However, the response of marine organisms to PAH exposure varies widely in nature, owing to variation in bioavailability.
  • Taxonomic groups with poorly developed mixed function oxygenase (MFO) capability. Do not metabolize the compounds efficiently. Hence, PAHs readily accumulate in these organisms, and they are often used as bio-monitors of PAH contamination in coastal waters.
  • Fish exposed to PAHs commonly develop lesions and tumors, and some investigators have reported a correlation between tissue levels of PAHs and neoplasia in mollusks.
  • Bacteria oxidize PAHs to carbon dioxide and water and in the process produce dihydrodiols and catechols.
  • Marine community changes caused by individual PAHs are more difficult to delineate than those generated by oil spills.
  • This is so because PAHs affect organisms through multiple pathways (e.g., physical contact, smothering, toxic action, and habitat modification).
  • Although acute lethal effects associated with elevated PAH level (e.g., local mass fish kills) have been rarely observed in nature, sub-lethal effects manifested at much lower concentrations are a chronic problem in some regions.
  1. Halogenated Hydrocarbons

Sources